Minimally invasive screw with double threaded plugs

Abstract

A minimally invasive screw with double threaded plugs is provided, for connecting to a connecting rod. The screw includes an inner threaded plug, an outer threaded plug, a lengthened arm connector, a press block and a pin with a hollow ball head. The connecting rod can be fixed to the lengthened arm connector via the press block, the inner and outer threaded plugs, to prevent the vertebral body from rotating and loss of intervertebral height when the vertebral body is distracted and pressurized.

What is claimed is: 
     
       1. A minimally invasive screw with double threaded plugs, connecting to a connecting rod, comprising:
 an inner threaded plug, 
 an outer threaded plug, 
 a lengthened arm connector including an inner wall, an outer wall, and an end, 
 a press block and 
 a pin with a hollow ball head, 
 wherein, the lengthened arm connector has a hollow interior, the connecting rod is configured to pass transversely through the lengthened arm connector, the outer threaded plug is movably disposed inside the lengthened arm connector, the inner threaded plug is movably disposed inside the outer threaded plug and is tightened relative to the outer threaded plug to make the connecting rod be fixed on the lengthened arm connector, and the press block is disposed on the inner wall of the lengthened arm connector to make the pin be fixed to the end of the lengthened arm connector to make the pin be locked within the range of motion when the outer threaded plug is tightened relative to the lengthened arm connector and thereby contacts and applies an external force on the press block; 
 wherein a lower part of the inner threaded plug has a protrusion for engaging with the connecting rod, to lock the connecting rod in the lengthened arm connector, and wherein the inner threaded plug and the outer threaded plug are configured to be independently tightened in two steps to lock the pin in position and to independently lock the connecting rod in position; 
 wherein at least one pair of a first positioning groove is symmetrically arranged on the outer wall of the lengthened arm connector, the press block is provided with a second positioning groove, the second positioning groove and the first positioning groove are co-axially arranged such that the pin can be fixed to the end of the lengthened arm connector when an external force is applied and the first positioning groove and the second positioning groove are thus passed through. 
 
     
     
       2. The minimally invasive screw with double threaded plugs of  claim 1 , wherein an upper part of the inner threaded plug is provided with a mounting groove for withstanding an external force to make the inner threaded plug rotate inside the outer threaded plug. 
     
     
       3. The minimally invasive screw with double threaded plugs of  claim 2 , wherein the mounting groove is a hexagon socket. 
     
     
       4. The minimally invasive screw with double threaded plugs of  claim 1 , wherein the outer threaded plug is provided with at least one opening for withstanding an external force to cause the outer threaded plug to rotate within the lengthened arm connector. 
     
     
       5. The minimally invasive screw with double threaded plugs of  claim 4 , wherein three openings are provided such that forces applied on the outer threaded plug are uniform while the inner threaded plug is rotating within the outer threaded plug. 
     
     
       6. The minimally invasive screw with double threaded plugs of  claim 1 , wherein at least one of the outer wall and the inner wall of the lengthened arm connector includes a groove for breaking the lengthened arm connector off in surgery. 
     
     
       7. The minimally invasive screw with double threaded plugs of  claim 6 , wherein the groove is disposed on a middle-upper part of an internal thread of the lengthened arm connector. 
     
     
       8. The minimally invasive screw with double threaded plugs of  claim 1 , wherein the outer wall and the inner wall of the lengthened arm connector include corresponding grooves, which are co-axially arranged, for breaking the lengthened arm connector off in surgery. 
     
     
       9. The minimally invasive screw with double threaded plugs of  claim 1 , wherein an interior of the pin with the hollow ball head has a through hole. 
     
     
       10. The minimally invasive screw with double threaded plugs of  claim 8 , wherein the grooves are disposed on a middle-upper part of the lengthened arm connector.